Single player RPGs are just constrained writing exercises, the same way single player DMimg is just writing a book. I actively play in my campaign as a player,

Single player RPGs are just constrained writing exercises, the same way single player DMimg is just writing a book. I actively play in my campaign as a player, but spend a lot of spare time writing campaign settings I never intend to play. It's a blend of creativity and fun which most good hobbies have.